First off, I'm a new member since a friend gave me his S400 Classic .177, 2007.

So far I've only managed a couple of hours plinking in a friend's garden 15 yds max as the club in Basingstoke has closed its membership at least until September. The gun came with a Bushnell scope , which I found impossible with my ageing eyesight. With or without glasses I had to chose between having the target or the reticle in focus. Reading up on the subject, it seems that the Objective is quite probably parallax free at 100 yds. So I'm now waiting for the courier with an Airmax scope (hopefully one issue sorted). Of course it will probably turn out that I'd have been fine with my reading glasses...

Other issues that have come up is that when pumped to 190 bar (yes I was sweating a bit) on the Hills pump's gauge, the AA gauge only read 160 bar. Now I'm perfectly happy to accept that these are fairly cheap innacurate gauges on the guns and mine is old enough to be of dubious usefulness. I can live with that, but it does restrict my ability to try to work out a power curve if I don't know the actual pressure once I go above 150 bar. I'm also waiting on delivery of a chrono so as to check it out in more detail. I guess once I have the chrono I shall have to extrapolate from the range in which the gauge is functional. Bearing in mind that the gauge is likely to be inaccurate anyway, that's not such a great loss.

Obviously what comes next will depend on what results I get. On the plus side, the gun is old enough that it doesn't have anti-tamper devices (anyone know when they started?). It also means that if the power is on the high side, I can take out the cover screw to tweak it down. Question: what lurks beneath the cover screw? I can see another allen head, but which way does it work? It seems far more likely that unless I strip and clean the hammer and rail it'll be on the low side and I wouldn't want to use it for that - better to strip and clean and see if that brings it back to spec. Another plus, I believe, is that the firing valve is likely to be of the old sort (hard nylon, I believe) so isn't quite the consumable item the new one is said to be.

On the subject of power, as the gun came with a full tube of AA field pellets I may never need buy more in my lifetime. But what maximum power setting would people advise? Set to 12fpe with my chosen pellet would certainly make it a failure if checked with a heavier projectile that Plod happened to have lying around. Is there a maximum pellet weight which can be chambered? I know in the USA they mould solid, full ogive bullets for airgun use, but then they have full-power to fire them and no restrictions of power allowed. Indeed, some suggest that dieselling is the only way to achieve acceptable performance. It strikes me we have another piece of legislation written by people who don't really understand the subject matter. In the absence of any reasoned advice, I guess I 'll look at the heaviest currently available 177 pellet in the UK and calculate for that and then compensate down to my lightweight pellet. One or two unknown factors in the calculation though.

I was also toying with the idea that maybe one day I would fit a regulator. I know many people are against them, but I accept that they are properly used to lower the firing pressure to that of the minimum acceptable point on the power curve. Whilst my shooting is never likely to justify the potential for improved repeatability, it should allow the gun to be filled to max pressure yet not lose the first 20+ shots as fliers until it reaches the upper pressure of the sweet spot. In effect, it extends the flattened curve up to maximum, though can't do anything once you drop below the set pressure. The Altaros design seems the simplest for the end user, particularly as you can adjust the set pressure or swap back to the original internals. So much scope for tinkering that I'd have to get a larger garden.

Welcome to the forum!
I'll just comment on a couple of points.
Both gauges could be wrong.
25 quid or so will get you a new gun gauge or pump gauge.
If you know someone with a gun type dive bottle you can fill it on their gauge and compare.
Under the power screw cover should be just one slightly stiff m3 grub screw (1.5mm key) that screws out to increase power. Only do 1/4 turn at a time.
There is a slim chance someone has put in an extra m3 grub screw on top of the adjuster to lock it.
I would set to 11 ft lbs no higher. It will kill a bunny as well as 12.
Forget dieseling this is a pcp.

Last edited by TenMetrePeter on Sun Jul 22, 2018 10:41 am, edited 1 time in total.

So many questions...
First the scope. As a quick fix you may be able to adjust the objective by heating the objective mounting and unscrewing. Focus the reticle first - against the sky - so you get sharpest definition when you open your eye. Then adjust the objective. I've used an electric paint stripping gun, first protecting the lens by cutting some cardboard discs. I don't know this scope but there are typically three parts that could move - an outer locking ring, an inner adjustment ring and the whole objective assembly including the lens. If the whole assembly moves you will have an AO scope! (Downside is air will leak into the scope unless you seal the threads. Don't unscrew fully and let air in!) If the lock ring moves take it off and unscrew the next component by about 1/2 turn and check for focus and parallax; adjust until set to preferred distance then put the lock ring back on.

Good advice from Peter. In the meantime don't worry too much about accuracy of gauges, I'd go by the Hills pump rather than the gun, Fill to 190 and chrono a full string - until velocity starts to fall away quite sharply. See what part of the curve you want to work with. Hopefully the 190 bar (according to Hills) will be higher than start of your sweet spot. When you go to fill the gun again read the end of string cylinder pressure from the Hills gauge. The fist few pumps (typically 5 or 6) will fill the whip (pressure will rise in big steps with each pump) and then the pressure increase per stroke will be small increments (read this pressure). If you assume a linear pressure drop vs shot count you can work out roughly what Hills pressure you need to get to the start of your sweet spot/chosen range.

Pellets: highest power will probably be with JSB Heavies (10.34gr). I've not found any pellet to exceed them in my 4 PCPs. JSBH will be around 0.5 ft lb higher than highest reading with AADF/JSB Exact 8.44gr and maybe 1ft lb higher than AA/JSB Express (7.87gr). You can easily get 0.2-0.3 ft lb variation between JSB die numbers - 8.44gr seem to vary more than 10.34gr. So if you are setting power with 8.44gr you will be looking for max 11.2-11.4 ft lb, (I'd still check with JSBH to be sure.)

Once you have found a pellet or pellets than suit your gun you can adjust for vertical stringing by knowing where you are on the power curve. Adjustment only really becomes necessary at ranges beyond maybe 30m. It helps to have a pressure gauge, or you can adjust by shot count. I have regged and unregged guns - with more predictable velocities from my unregged S400 than from a regged Weihrauch - by that I mean less variation over a 10-20 shot string. But need to make a small adjustment (2-3 clicks) between 190 and 160 bar on the S400 if I want to use the full capacity.

I wouldn't bother regging an S400 Classic. A carbine, perhaps, to increase the shot count. My S510 US is Altaros regged, which is great when set up correctly but needs to be adjusted periodically.